1. Field of the Invention
This invention relates to a nitride semiconductor epitaxial wafer and a field effect nitride transistor.
2. Description of the Related Art
In conventional art, nitride semiconductors containing indium (In), gallium (Ga), aluminum (Al), nitrogen (N) and the like have been being developed and put into practical use as materials for innovative high-efficiency light emitting devices which cover most of ultraviolet to visible light regions, by controlling a group III element composition ratio therein.
In addition, the nitride semiconductors have been put into practical use as materials for electronic devices to achieve high efficiencies and high outputs in high frequency regions, because of having high saturation electron velocity and high dielectric breakdown voltage.
JP-A-2009-32713 discloses a nitride semiconductor transistor in which a channel layer is formed of GaN, and which has a cap layer whose lattice constant is greater than that of GaN, so that when electrons in the channel formed in a heterojunction structure are accelerated, they are not easily trapped at a surface level.
JP-A-2010-272887 discloses a group III nitride semiconductor device in which a lattice constant in an a-axis of a buffer layer is smaller than a lattice constant in an a-axis of bulk AlN, in order to enhance the homogeneity of the buffer layer, and enhance the crystallinity of the group III nitride semiconductor formed over the buffer layer.
Refer to JP-A-2009-32713 and JP-A-2010-272887.